Silicone elastomers are generally stable at temperatures below about 150.degree. C. and may be used at temperatures up to about 260.degree. C. and even up to 315.degree. C. for short periods of time. When these same silicone elastomers are used at temperatures above about 200.degree. C. for extended periods of time, they have a tendency to deteriorate rapidly. Since silicone elastomers are generally used at elevated temperatures in many of their applications, deterioration is a highly undesirable property.
It is known that metallic compounds can be incorporated in silicone elastomers to enhance their heat stabilty. For example, U.S. Pat. No. 2,759,904 to Talcott discloses incorporating an iron salt of a carboxylic acid into a heat curable organopolysiloxane composition to form silicone elastomers to impart heat stability thereto. Also, Talcott discloses in U.S. Pat. No. 2,999,076, adding a carboxylic acid salt of cobalt, cerium or copper to an organopolysiloxane composition to impart heat stability properties thereto. Likewise, Brown et al disclose in U.S. Pat. No. 3,082,181 the addition of a carboxylic acid salt of iron, cobalt or manganese to an organopolysiloxane composition to improve heat resistance of the silicone elastomers. U.S. Pat. No. 3,142,655 to Bobear discloses incorporating rare earth compounds in organopolysiloxane compositions to improve their resistance to heat aging.
Although the metallic compounds described above improve the heat stability of the organopolysiloxane compositions, it has been found that when an amorphorus silica is used as a filler in the organopolysiloxane compositions, the resultant compositions exhibit a substantial reduction in the tensile strength and durometer.
Therefore, it is an object of this invention to provide heat curable silicone elastomers having improved heat stability. Another object of this invention is to provide heat curable silicone elastomers having improved retention of tensile strength and durometer. A further object of this invention is to provide a method for improving the heat stability of heat curable silicone elastomers. A still further object of this invention is to improve the resistance of silicone elastomers to reversion.